JPH07150493A - Method for bleaching chemical paper pulp - Google Patents

Abstract

PURPOSE: To provide a novel sequential bleaching process by which cellulose is not damaged excessively and by which high whiteness can be attained or whiteness of the bleached pulp can be improved. CONSTITUTION: A chemical paper pulp is bleached by means of a sequential treatment stages involving a state with at least one peroxyacid and a stage with an enzyme produced from bacterium of BaCillus genus, preferably xylanase, in any order. The above-mentioned two stages may be carried out continuously or carried out with interposition of one or more bleaching stage(s) without using peroxy acid nor enzyme (such as chlorine bleaching, oxygen bleaching and alkaline extraction). As a peroxyacid, org. or inorg. peroxyacids such as poroxyacetic acid, 1,6-diperoxyhexane diacid, triperoxycitric acid and peroxymonosulfuric acid are used in an amount of 1-5 wt.% expressed as H2 O2 equivalent to the dry pulp. It is preferable that the above-mentioned enzyme does not contain any cellulase destroying cellulosic polymer chains.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for bleaching chemical paper pulp.

[0002]

2. Description of the Prior Art Unbleached chemical paper pulp obtained by digesting cellulosic material in the presence of chemical reactants is not treated by a series of delignification and bleaching steps involving the use of oxidizing chemicals. It is known. The purpose of the first step of the conventional series of bleaching of chemical pulp is to complete the delignification of the unbleached pulp as it is in the finished cooking operation. This first delignification step treats the unexposed pulp conventionally with chlorine in an acidic medium or with chlorine / chlorine dioxide as a mixture or continuously and reacts with the lignin remaining in the pulp. And chlorolignin which can be extracted from the pulp by dissolving in an alkaline medium in a subsequent treatment step. For various reasons, it has been found useful in some circumstances to replace this first delignification step with a treatment that no longer requires a chlorine-containing reactant.

Approximately 20 years ago, it was proposed to carry out a process using gaseous oxygen in an alkaline medium before the first treatment step with chlorine or a chlorine / chlorine dioxide combination (New York in 1982). Encyclopedia of Che by Kirk-Othmer published in the state
mical Technology, 3rd Edition, Vol. 19, page 415, section 3 and page 416, section 1 and 2). However, when the purpose is to produce a chemical pulp with high whiteness without impairing the mechanical properties, the delignification degree obtained by this oxygen treatment is not sufficient. A method of bleaching sulfite or sulfate pulp with high strength hydrogen peroxide in the presence of sodium silicate has been proposed (J. May 1992).
HC-Peroxidbleiche fur Zellst by Kappel
off, Wochenblatt furPapierfabrikation Volume 120 Volume 9
No. 328-334). However, even if a sufficient amount of hydrogen peroxide of 3 g or more per 100 g of dry pulp is used, it is difficult to finally obtain the whiteness higher than 85 ° ISO by this method.

[0004]

SUMMARY OF THE INVENTION The present invention provides a novel series of known bleaching procedures which can achieve high whiteness or improve whiteness of bleached pulp without excessively damaging the cellulose. The disadvantages of these known processes have been overcome by providing a process for delignifying and / or bleaching chemical paper pulp.

[0005]

Therefore, the present invention is produced from one or more kinds of step (step Å) using one or more peroxyacids and Bacillus genus bacteria, which are carried out in any order. It relates to a method of bleaching a chemical paper pulp by a series of treatment steps including a step (step X) using an enzyme.

Chemical paper pulp means pulp which has been delignified in the presence of a chemical reactant such as sodium sulfide in an alkaline medium, sulfur dioxide or a metal salt of sulfurous acid in an acidic medium (respectively, Kraft or sulphate cooking, and sulphite or bisulphite cooking). The term also refers to chemical-mechanical and semi-chemical pulps (neutral sulfite cooks, also known as NSSC cooks), such as those cooked with salts of sulfite in neutral media (this pulp is also Bleached by the method of the invention), and Ullmann's Encyclopedia of Industrial
Chemistry, 5th Edition, Volume A18, 1991, 568-5
Also meant are pulps obtained by methods using solvents such as Organosolv, Alcell®, Organocell® and Asam pulps described on page 69. The invention applies in particular to pulp which has been kraft or sulphite cooked. All kinds of wood used for the production of chemical pulp are suitable for use in the process of the invention, especially those used for kraft and sulphite pulp, i.e. softwood wood such as various pine and fir, and beech, for example. Suitable for deciduous wood such as oak, eucalyptus and hornbeam.

According to the present invention, the step Å using a peroxy acid comprises one or more hydroperoxy groups --O-- in the molecule.
It refers to the step of using an acid containing OH or an ammonium salt or metal salt of this acid. The peroxyacids according to the invention belong to the peroxyacid family, whether organic or inorganic. According to the first aspect of the invention, the peroxy acid is an organic peroxy acid. Organic peroxy acids according to the present invention are selected from performic acid and aliphatic, cycloaliphatic or aromatic peroxy acids. When the peroxy acid is an aliphatic peroxy acid, it is selected from peroxy acids containing 1 to 3 percarboxylic groups. Aliphatic peroxy acids containing one percarboxyl group preferably contain linear or branched saturated alkyl chains of less than 11 carbon atoms, most preferably less than 6. Examples of such peroxyacids are peroxyacetic acid, peroxypropanoic acid,
Peroxybutanoic acid and peroxypentanoic acid.
Peroxyacetic acid is particularly preferred because it is nontoxic and the preparation is relatively simple.

The aliphatic peroxy acids containing 2 and 3 percarboxylic groups according to the invention are selected from linear or branched di- and triperoxycarboxylic acids containing less than 16 carbon atoms. In the case of diperoxycarboxylic acids, it is preferred that two percarboxylic groups be substituted on the carbon atoms located in the α- and ω-positions relative to each other. Examples of such diperoxycarboxylic acids are 1,6-diperoxyhexanedioic acid, 1,8-diperoxyoctanedioic acid, 1,
They are 10-diperoxydecanedioic acid and 1,12-diperoxidedecanedioic acid. An example of triperoxycarboxylic acid is triperoxycitric acid. The aromatic peroxy acids according to the present invention are selected from those containing one or more percarboxylic groups per benzene ring. Preferably the aromatic peroxy acid is selected from those containing one percarboxyl group per benzene ring. An example of such an acid is peroxybenzoic acid. Another aspect of the method according to the invention is to select an organic peroxy acid substituted with any organic functional substituent. By organofunctional substituents is meant functional groups such as alcohol-containing, nitrogen-containing groups such as nitrile, nitro, amine and amide groups and sulfur-containing groups such as sulfo and mercapto.

According to a second embodiment of the present invention, the peroxy acid is an inorganic peroxy acid. The inorganic peroxy acids according to the present invention may contain one or more peroxy groups. However, inorganic peroxy acids containing one peroxy group are preferred. Examples of such inorganic peroxyacids are peroxysulfuric acid, selenic acid, telluric acid, phosphoric acid, arsenic acid and silicic acid. Good results have been obtained with peroxymonosulfate, also known as caroic acid. Mixtures of different organic and / or inorganic peroxy acids are also well suited. The consistency of the pulp in the treatment step with peroxyacid is generally 3% by weight or more of solids, preferably 5%.
% Or more solids. In many cases, the consistency does not exceed 50% by weight solids, preferably 40% solids. In the process according to the invention, the amount of peroxyacid used is selected as a function of the amount of lignin remaining in the pulp and the average time of treatment. In general, an amount of peroxyacid of 0.1% by weight or more, preferably 1% by weight or more, of active oxygen expressed as H ₂ O ₂ equivalent to dry pulp is well suited. H for dry pulp
Often an amount of peroxyacid of not more than 10% by weight of ₂ O ₂ equivalent of active oxygen, preferably not more than 5%, is used.

Another embodiment of the process according to the invention carries out the process with peroxyacid in the presence of a stabilizer. Known stabilizers of peroxylated products are well suited. Examples of such stabilizers are alkaline earth metal salts (especially soluble magnesium salts), soluble inorganic phosphates and polyphosphates (eg pyrophosphoric acid or metaphosphoric acid alkali metal salts), silicic acid alkali metal salts, organic poly salts. Carboxylic acids (eg tartaric acid,
Citric acid, gluconic acid, diethylenetriaminepentaacetic acid or cyclohexanediaminetetraacetic acid) and their soluble salts, poly (α-hydroxyacrylic acid) and their soluble salts, and organic polyphosphonic acids (eg ethylenediaminetetra (methylenephosphonic) acid, diethylenetriaminepentaacetic acid). (Methylenephosphonic acid) or cyclohexanediaminetetra (methylenephosphonic acid)) and their soluble salts. It is also possible to combine a plurality of these stabilizers as a mixture. The stabilizer is preferably selected from phosphoric acid and salts thereof. Preferably, (1-hydroxyethylidene) diphosphonic acid (HEDPA)
, Ethylenediaminetetra (methylenephosphonic) acid (ED
TMPA), diethylenetriamine penta (methylenephosphonic) acid (DTMPA), triethylenetetramine hexa (methylenephosphonic) acid (TTHMPA), pentaethylenehexamine octa (methylenephosphonic) acid (PHOMPA), cyclohexanediaminetetra (methylenephosphonic) acid (CDTMPA) ) And nitrilotri (methylenephosphonic) acid (NTMPA). DTMPA and its salts provided excellent results. The total amount of stabilizer used depends on the type of wood used and the cooking process. Generally, 0.05 based on solids content
It is recommended to use at least wt%, preferably at least 0.2 wt% stabilizer. 3% by weight based on solids content,
Preferably an amount not exceeding 2% by weight is generally sufficient. The treatment with peroxyacids according to the invention can also be carried out in the presence of multiple stabilizers used as a mixture.

According to the invention, step X of treating with one or more enzymes is the treatment of pulp with a composition containing one or more enzymes. Enzymes have already been subjected to one or more steps of bleaching using unbleached chemical paper pulp produced by the digestion process or oxidizing reactants such as oxygen, hydrogen peroxide and ozone, depending on the steps after the treatment step using the enzyme. By any enzyme capable of promoting delignification of applied chemical paper pulp. Preference is given to using alkalophilic enzymes, ie enzymes which show maximal efficiencies in the alkaline pH range, in particular at pH above 7.5. A type of enzyme that is well suited for the method according to the invention is hemicellulase. These enzymes can react with the lignin-bound hemicellulose present in the pulp. The hemicellulase used in the method according to the invention is preferably xylanase. That is, an enzyme that hydrolyzes hemicellulose capable of cleaving the xylan bonds that make up most of the interface between lignin and other carbohydrates. An example of a xylanase according to the method according to the invention is 1,4-β-D-Xylanxylanohydrolase, EC 3.2.1.8.

The preferred sources of xylanase production in the method according to the invention vary. Especially in a wide range
Produced by Bacillus bacteria. Bacillus and pumi
Excellent results have been obtained with xylanase produced from lus species. Of these, Bacillus pumilu
Xylanase produced from s PRL B12 is particularly advantageous. The xylanase produced from Bacillus pumilus PRL B12 according to the present invention may be produced directly from a strain of Bacillus pumilus PRL B12, or may already be genetically expressed to represent the gene of Bacillus pumilus PRL B12 encoding xylan degradation. It may be produced from a host strain of a different microbial engineered. Preferably, a purified xylanase containing no other enzyme is used. In particular, the xylanase according to the method according to the invention does not contain any cellulase since it does not break the cellulosic polymer chains of the pulp.

An advantageous embodiment of the process according to the invention carries out step X in the presence of one or more sequestering agents. The sequestering agent may be advantageously selected from the peroxy acid stabilizers mentioned above. According to the invention, step Å and step X can be carried out in any order in the bleaching step. It may be carried out continuously or may be carried out separately in one or more other known bleaching steps. Step Å or step X may be carried out at any time, either at the start or at the end of the bleaching step. The process according to the invention starts with the first step using chlorine in an acidic medium or chlorine in combination with chlorine dioxide in an acidic medium (successive introduction of a mixture of Cl ₂ and ClO ₂ or two reactants). It can be used in conventional bleaching methods. A preliminary step with oxygen may also be carried out before the step with chlorine in acidic medium or with chlorine in combination with chlorine dioxide in acidic medium. In these methods, it is possible to reduce the amount of chlorine and / or chlorine dioxide while maintaining the same final whiteness of the pulp produced. An example of such an order is C _D E _P Å _P
XDP, C / DE _P Å PXDP, OC _D E _P Å PXD
P, OC / DE _P Å PXDP, C _D XQP Å _P , C / D
XQPÅP, OC _D XQPÅP, OC / DXQPÅP,
C _D XEDPÅ, C / DX EDPÅ, OC _D XEDP
Å or OC / DXEDPÅ. The abbreviations used have the following meanings.

Å: Process using peroxyacid according to the present invention C: Process using chlorine in acidic medium _D : Process using chlorine dioxide C _D : Process using chlorine in combination with chlorine dioxide in acidic medium (Reactant is continuously introduced into pulp) C / D: Process using chlorine and chlorine dioxide introduced into pulp as a mixture E: Alkali extraction process using alkali metal or alkaline earth metal hydroxide E _P : Hydrogen peroxide-enhanced alkali extraction step P: Step using hydrogen peroxide in an alkaline medium Q: Step using one or more sequestering agents X: Step using the enzyme according to the present invention

The process according to the invention also comprises an elemental chlorine-free bleaching step (known as ECF or "elemental chlorine-free") or a completely chlorine-free bleaching step (TCF or "totally". Especially suitable for chlorine-free "). In this type of process, the purpose of reducing the amount of chlorine used to reduce decomposition of pulp is more easily achieved in order to obtain a whiteness equal to or higher than the final whiteness obtained by the conventional method. You can. Examples of the ECF process according to the present invention are XÅPDP, XÅDPD, XÅPDPD, XO.
PÅP, XPÅ PDP, OXPÅ PDP, DE _P ÅPX
DP, ODE _P Å PXDP, DXQP Å _P , ODXQP
ÅP, DXEDPÅ or ODXEDPÅ. Examples of TCF process according to the present invention, X / QPÅP, X / QE O Å
P, X / QE _OP ÅP, OX / QPÅP, OX / QE _O Å
P, OX / QE _OP ÅP, X / QÅE _P P, OX / QÅE
_{P P, X q PÅP, X} q E O ÅP, X q E OP ÅP, OX
_q PÅP, OX _q E _O ÅP, OX _q E _OP ÅP, X / Q Å
PÅP, X / QÅPP or OX / QÅPP. In these steps, step X / Q or X _q is separated into two separate steps X and Q (optionally by washing, eg O 2
QXPÅP and OXQPÅP in either order (Q
X or XQ))).

In these examples, the abbreviations X _q and X
/ Q is a step of introducing the enzyme into the pulp first, and then introducing one or more sequestering agents without washing the pulp after a certain reaction time, and the enzyme and 1
It means a process of simultaneously introducing one or more sequestering agents into pulp. The abbreviation E _O means an alkali extraction step which is fortified by the presence of oxygen, and the abbreviation E _OP means a similar step in which a small amount of hydrogen peroxide is mixed in addition to oxygen. Good results were obtained with the steps OX / QPP _aa P and OX _q PC _A P. In these steps, the abbreviations P _aa and C _A mean the step using peracetic acid and the step using peroxymonosulfate, respectively.

[0017]

EXAMPLES The following examples are provided to illustrate the present invention without limiting its scope. Examples 1R and 2R (not according to the invention) Samples of kraft cooked deciduous pulp (ISO standard 24
Initial whiteness of 27.9 ° ISO measured by 70-1977 (F)
, S value of 26.7 measured by SCAN standard C1-59, and S
Degree of polymerization 1680) represented by the number of glucose units, measured by CAN standard C15-62, was measured by 5 steps OQ under the following conditions.
They were treated according to the order of the PC _A P. The first step: a step using oxygen (Step O): Pressure (bar): 6 NaOH content (g / 100 g of dry _{pulp): 4 MgSO 4 · 7H 2} O content (g / 100 g of dry pulp): 0.5 Temperature (℃ ): 120 hours (min): 60 Consistency (% by weight of solids): 12 Second step : Step using DTPA (step Q): DTPA content (g / 100g dry pulp): 0.2 Temperature (° C): 50 Hours (min): 105 at pH 7, then 15 at pH 5.5 Consistency (wt% of solids): 3

Third step : Step using hydrogen peroxide (step P): H ₂ O ₂ content (g / 100 g dry pulp): 1 NaOH content (g / 100 g dry pulp): 1.6 Na ₇ DTMPA content (g / 100g of dry _{pulp): 0.025 MgSO 4 · 7H 2} O content (g / 100g dry pulp): 0.2 temperature (° C.): 90 hours (minutes): 120 consistency,% by weight of solids: 10 the Na ₇ DTMPA is , Hepta sodium salt of diethylenetriaminepenta (methylenephosphonic) acid. Fourth step : Step using caroic acid (step C _A ): H ₂ SO ₅ content (g / 100 g dry pulp): 3 (Example 1R) or 4.5 (Example 2R) Na ₇ DTMPA content (g / 100 g) dry _{pulp): 0.025 MgSO 4 · 7H 2} O content (g / 100 g of dry pulp): 0.2 initial pH: 4 to 5 temperature (° C.): 90 hours (minutes): 120 consistency,% by weight of solids: 10

Fifth step : Step using hydrogen peroxide (step P): H ₂ O ₂ content (g / 100g dry pulp): 2.0 NaOH content (g / 100g dry pulp): 1.6 Na silicate at 38 ° Be content (g / 100 g of dry _{pulp): 3.0 MgSO 4 · 7H 2} O content (g / 100 g of dry pulp): 1.0 temperature (° C.): 90 hours (minutes): 240 consistency,% by weight of solids: 30 after treatment At the end of the process, the κ number, degree of polymerization and whiteness of the pulp were measured. The κ number was also measured after the third step (step P).

[0020]

[Table 1] Table 1 Example number Final whiteness κ number after P1 Final κ number Final polymerization degree ° ISO 1R 89.8 6.4 1.6 960 2R 91.4 6.6 1.2 930 In the table, P1 represents the first P (third process) in the process.

Examples 3 and 4 : (according to the invention) A sample of the same pulp as in Examples 1R and 2R was used in step X in an amount of Ba corresponding to 10 XU / g dry pulp.
Bleaching was performed using xylanase produced from Cillus pumilus PRL B12 in the order of OX _q PC _A P. Unit XU (xylanase unit) is 1 in reducing capacity under test conditions
It is defined as the amount of xylanase that catalyzes the release of reducing sugars corresponding to 1 μmol glucose per minute. The working conditions were as follows. The first step: a step using oxygen (Step O): Pressure (bar): 6 NaOH content (g / 100 g of dry _{pulp): 4 MgSO 4 · 7H 2} O content (g / 100 g of dry pulp): 0.5 Temperature (℃ ): 120 hours (min): 60 Consistency (% by weight of solids): 12 Second step : Step using enzyme xylanase and DTPA (step X _q ): First phase: enzyme only Xylanase content (XU / g Dry pulp): 10 Temperature (° C): 50 hours (min): 105 Consistency (wt% of solids): 3 pH: 7 Second phase: DTPA (without intermediate washing) DTPA content Content (g / 100g dry) Pulp): 0.2 Temperature (℃): 50 hours (min): 15 Consistency (% by weight of solids): 3 pH: 5.5

Third step : Step using hydrogen peroxide (step P): H ₂ O ₂ content (g / 100 g dry pulp): 1 NaOH content (g / 100 g dry pulp): 1.6 Na ₇ DTMPA content (g / 100g of dry _{pulp): 0.025 MgSO 4 · 7H 2} O content (g / 100g dry pulp): 0.2 temperature (° C.): 90 hours (minutes): 120 consistency,% by weight of solids: 10 the Na ₇ DTMPA is , Hepta sodium salt of diethylenetriaminepenta (methylenephosphonic) acid. Fourth step : Step using caroic acid (step C _A ): H ₂ SO ₅ content (g / 100 g dry pulp): 3 (Example 3) or 4.5 (Example 4) Na ₇ DTMPA content (g / 100 g) dry _{pulp): 0.025 MgSO 4 · 7H 2} O content (g / 100 g of dry pulp): 0.2 initial pH: 4 to 5 temperature (° C.): 90 hours (minutes): 120 consistency,% by weight of solids: 10

Fifth step : Step using hydrogen peroxide (step P): H ₂ O ₂ content (g / 100g dry pulp): 2.0 NaOH content (g / 100g dry pulp): 1.6 Na silicate at 38 ° Be content (g / 100 g of dry _{pulp): 3.0 MgSO 4 · 7H 2} O content (g / 100 g of dry pulp): 1.0 temperature (° C.): 90 hours (minutes): 240 consistency,% by weight of solids: 30 after treatment At the end of the process, the κ number, degree of polymerization and whiteness of the pulp were measured. The κ number was also measured after the third step (step P). The obtained results were as follows.

[0024]

[Table 2] Table 2 Example number Final whiteness κ number after P1 Final κ number Final polymerization degree ° ISO 3 91.7 5.6 1.2 970 4 92.9 5.6 1.0 940 In the table, P1 represents the first P in the process (third process).

Example 5R (not according to the invention) Another sample of deciduous kraft pulp (ISO standard 2470-1977).
Initial whiteness measured by (F) 27.9 ° ISO, SCAN
Κ number measured by standard C1-59 26.7, and SCAN standard
The degree of polymerization represented by the number of glucose units of 1680) measured by C15-62 was measured under the following conditions in 5 steps OQPP _aa P
It processed according to the order of. The first step: a step using oxygen (Step O): Pressure (bar): 5.7 NaOH content (g / 100 g of dry _{pulp): 4 MgSO 4 · 7H 2} O content (g / 100 g of dry pulp): 0.5 Temperature (℃ ): 120 hours (min): 60 Consistency (% by weight of solids): 12 Second step : Step using DTPA (Step Q): DTPA content (g / 100g dry pulp): 0.16 Temperature (° C): 60 Time (minutes): 60 Consistency (wt% of solids): 5

Third step : Step using hydrogen peroxide (step P): H ₂ O ₂ content (g / 100 g dry pulp): 1 NaOH content (g / 100 g dry pulp): 1.3 Na ₇ DTMPA content (g / 100g of dry _{pulp): 0.025 MgSO 4 · 7H 2} O content (g / 100g dry pulp): 1 temperature (° C.): 90 hours (minutes): 120 consistency,% by weight of solids: 10 the Na ₇ DTMPA is , Hepta sodium salt of diethylenetriaminepenta (methylenephosphonic) acid. Fourth step : Step using peracetic acid (Step P _aa ): CH ₃ CO ₃ H content (g / 100 g dry pulp): 2 Na ₇ DTMPA content (g / 100 g dry pulp): 0.125 Temperature (° C): 90 Time (minutes): 360 Consistency (wt% of solids): 10

Fifth step : Step using hydrogen peroxide (step P): H ₂ O ₂ content (g / 100g dry pulp): 1 NaOH content (g / 100g dry pulp): 1 Na silicate at 38 ° Be content (g / 100 g of dry _{pulp): 3 MgSO 4 · 7H 2} O content (g / 100 g of dry pulp): 1 temperature (° C.): 80 hours (minutes): 360 consistency,% by weight of solids: 20 after treatment At the end of the process, the κ number, degree of polymerization and whiteness of the pulp were measured. The κ number was also measured after the third step (step P). The obtained results were as follows.

[0028]

[Table 3] Table 3 Example number Final whiteness κ number after P1 Final κ number Final polymerization degree ° ISO 5R 76.7 9.7 3.9 1050 In the table, P1 represents the first P in the process (third process).

Example 6 (according to the invention) A sample of the same pulp as in Example 5R
Bacillus pumilus PR in an amount corresponding to XU / g dry pulp
Using xylanase produced from L B12, OX / QP
_Bleached in order of PaaP. The working conditions were as follows. The first step: a step using oxygen (Step O): Pressure (bar): 5.7 NaOH content (g / 100 g of dry _{pulp): 4 MgSO 4 · 7H 2} O content (g / 100 g of dry pulp): 0.5 Temperature (℃ ): 120 hours (min): 60 Consistency (% by weight of solids): 12 Second step : Step using enzyme and DTPA (Step X / Q): Xylanase content (XU / g dry pulp): 5 DTPA content (G / 100g dry pulp): 0.16 Temperature (℃): 60 hours (min): 60 Consistency (wt% of solids): 5

Third step : Step using hydrogen peroxide (step P): H ₂ O ₂ content (g / 100 g dry pulp): 1 NaOH content (g / 100 g dry pulp): 1.3 Na ₇ DTMPA content (g / 100g of dry _{pulp): 0.025 MgSO 4 · 7H 2} O content (g / 100g dry pulp): 1 temperature (° C.): 90 hours (minutes): 120 consistency,% by weight of solids: 10 the Na ₇ DTMPA is , Hepta sodium salt of diethylenetriaminepenta (methylenephosphonic) acid. Fourth step : Step using peracetic acid (Step P _aa ): CH ₃ CO ₃ H content (g / 100 g dry pulp): 2 Na ₇ DTMPA content (g / 100 g dry pulp): 0.125 Temperature (° C): 90 Time (minutes): 360 Consistency (wt% of solids): 10 Fifth step : Step using hydrogen peroxide (P step): H ₂ O ₂ content (g / 100g dry pulp): 1 NaOH content (g / 100g of dry pulp): 1 38 ° Be Na silicate content (g / 100g dry _{pulp): 3 MgSO 4 · 7H 2} O content (g / 100g dry pulp): 1 temperature (° C.): 80 hours (minutes): 360 Consistency (wt% of solids): 20 After treatment, at the end of the process, the κ number, degree of polymerization and whiteness of the pulp were measured. The κ number was also measured after the third step (step P). The obtained results were as follows.

[0031]

[Table 4] Table 4 Example number Final whiteness κ number after P1 Final κ number Final polymerization degree ° ISO 6 79.2 8.7 3.2 1060 In the table, P1 represents the first P (third process) in the process.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Joan Devenin Belgium Bee 1020 Brussels Pronkerve Trahn 30 (72) Inventor Pierre Redou Belgium Be 1200 1200 Brussels Avenue D'Dix Arpant 100 (72) Inventor René Detro Belgium Be 1328 O'an Schose Druvin 534

Claims (10)

[Claims] 1. A method of bleaching a chemical paper pulp by a series of treatment steps, wherein the series of steps is carried out in any order, using one or more kinds of peroxy acid (step Å) A method comprising the above and one or more steps (step X) using an enzyme produced from a bacterium of the genus Bacillus . 2. The method of claim 1, wherein one or more bleaching steps free of peroxyacid and enzyme separate steps Å and X. 3. The method according to claim 1, wherein the peroxyacid- and enzyme-free bleaching step does not separate steps Å and X. 4. The method according to any of claims 1 to 3, wherein step X comprises one or more xylanase. 5. The method according to claim 1, wherein step X is carried out in the absence of cellulase. 6. The method according to claim 1, wherein the bacterium of the genus Bacillus is a bacterium of pumilus species. 7. The bleaching order is OQXPÅP, OXQPÅ
P, A method according to any one of claims 2 and 4 to 6 is selected from the order of the OX / QPÅP and OX _q PÅP. 8. The order of bleaching is OX / QPP _aa P, OX _q P
7. A method according to any of claims 2 and 4 to 6 selected from the order P _aa P, OX / QPC _A P and OX _q PC _A P. 9. The order of bleaching is OX / QP _aa P, OX _q P _aa
7. A method according to any of claims 3 to 6 selected from the order of P, OX / QC _A P and OX _q C _A P. 10. The method according to claim 1, which is used for bleaching kraft pulp.